I’ve been able to solve the problems so far. However, one thing remains that I consider to be a bug.
Objects that are duplicated in blender and then mirrored with Ctrl + M are displayed incorrectly in UE after being imported.
Reverse culling, two sided material, recompute normals etc. does not help. Depending on the viewing angle, the object has no front. You can almost see into the mesh.
If I turn the mesh in the blender manually, that doesn’t happen. Unfortunately, sometimes the geometry requires it to be mirrored.
After the light build, these objects are pitch black. If I activate -two sided materials-, the objects are only displayed correctly in the viewport. greetings